Using lipochromosomes (phospholipid entrapped metaphase chromosomes) we have transferred the human NGPRT, G6PD and PGK genes into a XCPRT deficient mouse cell line (A9). This novel technique increased the frequency of gene transfer to 1X10-5. We have now enzymatically analysed 14 of the transferent clones from two independent transfer experiments. Four clones out of 14 were analysed to see if a detectable human chromatin could be identified in their karyotype to account for the transferred genes. The data suggest that (i) substantial human chromosomal fragments can be transferred into recipient cells using lipochromosomes; (ii) clones from human HGPRT positive A9 transferent subpopulations may or may not possess other human X-linked markers; (iii) the stability of lipochromosomally transferred genes is variable during continuous maintenance in the minimal essential or HAT medium; (iv) when multiple X-linked human genes are transferred a cytologically detectable human chromatin was identified in the transferents free or attached to a host chromosome; and (v) integration of transferred human chromosomal material into mouse chromosomes may occur at preferential site(s) in the recipient genome.